A large proportion of patients who must be fitted with a denture and, particularly, with a full denture are aged persons. In general, further, the alveolar ridge shows such a large bone absorption that an increased force of occlusion must be born per a unit area. The alveolar ridge mucosa, too, becomes thin due to senile atrophy. Therefore, the shock due to occlusion and masticatory pressure is not relaxed but is directly transmitted to the alveolar bone. As a result, a thin mucosa sandwiched between the hard resin denture base and the hard alveolar bone is squeezed and gets scarred after every occlusion, and produces a pain.
In such a difficult case of disease, good results are not obtained for stably maintaining and supporting the denture even if the denture base is produced by using a commonly used (meth)acrylic resin only. Namely, it is necessary to line the surface of the denture base mucosa with a material having a suitable degree of elasticity, to compensate the lost viscoelasticity of the residual ridge mocusa and to impart cushioning property for relaxing the shock at the time of occlusion.
There has been favorably used a silicone rubber lining material of the room temperature vulcanizing type that cures at a temperature of up to 50° C. However, the silicone rubber lining material poorly adheres to the (meth)acrylic resin which is the denture base. Therefore, there have been developed several adhesives for adhering the (meth)acrylic resin which is the denture base with the silicone rubber material which is the lining material, and there has been known the one obtained by dissolving a particular acrylic copolymer having a silyl group in a suitable volatile organic solvent.
For example, there have been developed an acrylic copolymer using an alkyl (meth)acrylate and a (meth)acrylic acid dimethyl vinyl silylalkyl ester (Japanese Unexamined Patent Publication (Kokai) No. 43209/1990) and an acrylic copolymer using an alkyl (meth)acrylate and a (meth)acrylic acid dimethyl hydrogensilylalkyl ester (Japanese Unexamined Patent Publication (Kokai) No. 68007/1992).
They are used by applying soluble solvent solutions of the above resins onto the (meth)acrylic resin of the denture base followed by drying and, then, applying a room temperature vulcanizing (setting through the hydrosilylation reaction) silicone paste which is a dental lining material. During the setting and/or after the setting, however, they must be heated at about 80° C. for 20 to 30 minutes or longer to accomplish a sufficient degree of adhesion.
There have further been developed acrylic random copolymers modified with a silicone having a polyorganosiloxane group with an SiH reaction point on a side chain thereof (Japanese Patents Nos. 3105733 and 3107702). The adhesives using these particular acrylic random copolymers are useful being capable of considerably strongly adhering the acrylic resin which is the denture base and the silicone rubber material which is the lining material together at low temperatures of from about 20 to about 30° C. within several minutes.
However, it has been desired to further improve the adhering performance.
As the organic solvent for dissolving the above silicone-modified acrylic copolymers, in particular, there has been used a halogen-containing organic solvent and, chiefly, methylene chloride. Use of the above organic solvent helps exhibit excellent adhering performance.
In recent years, however, the halogen-containing organic solvents have been suspected of causing environmental disruption and toxicity. Though the truth has not yet been clarified, it is desired to avoid the use of halogen-containing organic solvents even in the dental materials.
Therefore, the adhesive is now using a halogen-free organic solvent such as ethyl acetate or ethyl methyl ketone to substitute for the halogen-containing organic solvent. In this case, the obtained adhesive exhibits excellent adhering force nearly equal to the halogen-containing organic solvent in the initial stage of adhesion accompanied, however, by such a defect that the adhering force greatly decreases with the passage of time lacking durability in the adhering force (durability of adhesion).
As the adhesive for the lining materials, further, there has further been known the one comprising the above silicone-modified acrylic copolymer and an organic solvent of a polymer of a particular (meth)acrylic acid ester having a carboxyl group for adhering the silicone rubber lining material and the metallic denture base (Japanese Unexamined Patent Publication (Kokai) No. 25292/1993). The above adhesive, however, is not still satisfactory for the use of adhesion since its adhering force to the (meth)acrylic resin denture base is not satisfactory.